Process for the manufacture of sulphuric acid of high purity



H. HOWARD 1,764,309 PROCESS FOR THE MANUFACTURE OF SULPHURIC ACID OF HIGH PURITY June 17, 1930.

Filed April 22, 1927 s June 1 1. .1930.

UNITED ,STATES: PATENT-[onion 7 mar nowAzm, or CLEVELAND, onro,

m emssnnm CHEMICAL COMPANY, DELAWARE ASSIGNOR, BY MESNE ASSIGNMENTS, TO

01 CLEVELAND, 9310, A CORPORATION 01' raocnss non THE MANUFACTURE or sunrmmrc Acm or men rum Application fi1ed Apri122, 1927'. Seriallio. 185,850.

process for the-manufacture. of sulphuric acid of high purity'had been developed and was in commercial use by the .Tentelevski Chemical Works'and some of the licensees of their contact process in Europe and in 1908 in thiscountry. By this process SO was obtained by heating oleum to about 260 C. .which drove off the S this S0,"

was condensed at such a temperature as to produce liquid S0 This product was then further purified by distilling it in a still heated by'low pressure steam (about atmospheric pressure) which, of course, gave S0 vapors entirely free from I-LSO or other nonvolatile impurities. This SO was then contacted with pure distilled water in a condenser made of some inert material, such as platinum, the Water being fed in a continu-' ous manner in phuric acid of run directly into the shipping containers,

usually. glass carboys.

. The acid so obtained is substantially chemically pure with the exception of a small amount of S0,, which remains dissolved in the acid. This was usually elimquantity suflicient to give sulinated by blowing purified air through the acid contained in the carboys.- But this proposition wasnot entirely satisfactory. If the acid is cold, it will require a considerable amount of air and time to free it from the dissolved sulphur dioxide; If the acid is run hot into the carboys and blown when still hot, there will be danger of breakage with all the serious inconveniences entailed thereby. Another disadvantage of thisprocess is that the'amount of the SO, vapors given ofl at eachtime during the distillation process varies and as it is practically impossible to regulate the flow of absorbing water to correspond to such variations, the acid received in the difierent successive carboys will likewise vary in strength. The usual solution of such a problem would, of course, be to run the production covering one or several periods of such recurring variations into a large single blending receiver. This, however, is not possible in the present case, as such a receiver would have to be made of an inert material, suchas platinum, gold,

the desired strength; this was such a receiver, even wouldmake the whole an apparatus which will allow of the contmuous production of substantially chemically pure sulphuric acid of reasonablyconstant concentration.

One object of my invention is to increase the efficiency of the absorption equipment by 30 allowing the absorption to proceed at comparatively high temperature and to purify; the still hot acid in a continuous manner.

My invention comprises distilling relatively pure liquid SQ as obtained by heat- 5 mg oleum to about260 '(l., as described above, and contacting the gaseous pure SO,

produced, with and absorbing it' n counter current in puredistilled water 1n such a,

manner that the SO comes in contact with strong sulphuric acid and the water with dilute acid and blowing the still hot sulphuric acid with heated, purified, and filtered air in a cascade apparatus in which the acidis successively contacted'with fresh portions of air. The purified acid is then passed through a cooler and run directly into the shipping containers, viz., glass carboys.

' A preferred process is to combine the sulphurlc acid as produced according to the above, and which may be of varying concentratlons,

from several such contacting units into a single flow. By combinin the acids I am able to produce an acid which, for all practical purposes, uniform-strength, the variations in the di ferent units compensating each other.

' y blowing the acid while still hot, I can easily-and economically free itfrom disis of sufiicientlfy 35 solved S0 -In doing it in successive steps,

the individual units will be small andcan be constructed from reasonably cheap material. The material will have to be resistant to moderate heat and to the action of strong or gold, but I 'found' sulphuric acid. Such units could, of course,

' basins could be built of glass by means of an overflow filled with strong sulphuric acid up i The blowing of the acid can be effected in various types of apparatus and shape of units, as, or instance, small towers, each tower receiving at the bottom a fresh supply of hot, pure air, the acid running from the bottom of .one tower, by gravity, for instance, upon the top of the ollowmg tower, or a cascade arrangement bein used, the or. sed silica,

the acid runnin I from one basin 1nto the next lower one, and fresh, pure air bubbled through the acid m each basin. Another convement form 'of blowing equipment will be described later on. I

' The purified acid is then finall passed through a cooler and runs into car oys,

I found a very practical equipment for racticing my invention to cons1s't of the ollowing arrangement, of which Figure 1 is a schematic elevation and Figure 2 a schematic plan view. A, in Figure 1, represents the aticsosed absorption apparatus; it is made of num or gold. It consists of a pipe at both ends. Pure distilled water enters at B; the water inlet is not tightly fitted into pi A so as to give an access to the atmosp ere. Pure gaseous SO, enters at C, the inlet pipe extending to near the bottom of pipe A. D is a dam and overflow which maintains a constant liquid level in ipe A. E is a curtain'extending below that level and preventing of gas from pipe A into t e tube F which leads the strong acid into 'a manifold G, to be described later, and can be omitted if constant strength of the acid produced is not essential.

Pipe A is set in abox'made of wood or any desired material, not shown in Figure 1, through which cold water is run to absorb the excess heat produced by the absorption of the SO in water, and the flow in it is so regulated that the concentrated acid produced leaves through pipe F at a temperature at which the succeeding purification by blowin with air is most efiiciently effected. he temperature of this acid is usually kept between and 80 C. For starting the operation, pipe A is to the level of dam Pure SO. and pure water are introduced simultaneously at the respective points; the sulphur trioxide comes in contact with strong acid which readily at D. Any S0 not immediately absorbed at the point of contact C travels in pipe A in contact with the liquid therein, and is gradually absorbed; the water entering at B mixes with the original acid and the diluted acid travels toward E at the rate at which the concentrated acid overflows at D and gradually increases in strength SO, as mi ht travel 'produced from heating oleum and any escapeabsorbs it and the acid overflows 4 through as it mixes with the strong acid roduced in the vicinity of C and-also a sorbs such above its surface. It will, there ore, be seen tha innormal o ation, pipe A will contain relatively di ute acid near- B and acid of increasing strength toward D; by regulat' the flow of water in proportionto the -S 3 introduced, a constant flow of concentrated acid will be'obtained at F. Some very important advantages of this arrangement are that the water comes in contact with dilute acid and the SO 'with strong acid only, preventing, in this manner,-any local violent reactions.

G is a manifold receiving and mixin the concentrated acid produced in severa absorbing units,

all of which have an independent supply in individual stills'distilling hquid SO, as

condensin the evolved SO... This manifold is convemently made of platinum or gold and, if desired, can be. set in a cooling box. It isadvisable, for a smooth-running of this equipment, to measure the strength of the acid at any oint between D and G, and this can done in a number of well known ways.

The manifold 'is arrangedto receive the strong acid roduced from an desired number of S a absorbing units, our being of pure SO, gas produced shown in Figure 2. The acid mixes therein, 7

and any variations in the strength of the acid produced in each unit are equalized.

The combined acids run in a single flow at a temperature of, say 50 to 60 0., either by gfavlty or, if the available spaces and heig -t of buildings require it, by an air lift or other pumping arrangement, into the first unit of the cascade purification system. This consists of a number of like units, three being shown in Figures 1 and 2; their number can fifteen to twenty-five units are suflicient.

.These units, represented by H, 11*, and H in Figures 1 and 2, are pyrex glass goosenecked flasks. The acid enters through the gooseneck into the bottom of the flas It meets then a current of hot, filtered air, and overflows by a side tube into the gooseneck of the next lower flask. The air bubbling through the dissolved traces of S0,. The air is introduced through a glass pipe I connected with a central air distribution line K.

The cascade blowing equipment is usually placed under a hood. The spent air, containin traces of. SO, as it escapes from each flask, is collected in the hood and led into astack.

The acid from the last flask is usually run a small cooler into the shipp' carboys, but as it will have had time to coo somewhat during the blowing process, the

be varied, but usually 4 hot acid entrains the cooler might be omitted without serious disadvantage.

Another and quite important advantage of this arrangement is that the whole operation can be carried on continuously, particularly where several absorption 'units are connected through the manifold. Disconnection of one or even several S0 distilling stills will not affect the purification step.

I claim:

The process of producing pure, concentrated sulphuric acid which comprises distilling liquid S0 absorbing the gaseous S0 in counter current arrangement in pure,

distilled water, in such a manner that the SOQcomes mainly in contact with strong sulphuric acid and the water with dilute acid, combining the concentrated acid produced in a plurality of absorbing units into a single flow and freeing the still hot acid from dissolved S0 by passing it in continuous flow through successive steps in each of which it is blown with fresh portions of air.

In testimony whereof, I affix my signature.-

HENRY HOW'ARI). 

